An industrial robot can normally operate in a manual mode and at least one automatic mode, which can usually be selected on the control unit of the manipulator. The manual operating mode is selected for the purposes of programming of the robot and, in this mode, the manipulator can be manoeuvred via commands imparted manually by an operator; in the automatic operating mode, instead, the movement of the manipulator is governed exclusively by its control unit.
The activity of programming of a robot with a number of degrees of freedom basically consists in teaching the robot the path that a point of its manipulator will have to repeat automatically in the course of the normal working steps, for carrying out a certain operation. This point is usually constituted by the so-called “Tool Center Point” (TCP), which identifies the position of the active part of an end effector of the manipulator, here understood as a machining tool or else as an ensemble consisting of a gripping device and the corresponding piece moved. The majority of the programming time is dedicated to governing the robot manually in order to identify the optimal points of the paths of movement of the TCP and store the corresponding coordinates thereof. For this purpose, a portable programming terminal, also known as “teach pendant” can be used, or else a manual guide device, directly mounted on the movable structure of the manipulator. It is also known to program an industrial robot in an off-line mode (Off-Line programming—OLP), using for the purpose a suitable program of a CAD type that simulates the working cell of the manipulator and that enables setting of the movements necessary for machining. Unlike the previous cases, this type of programming is performed substantially in a remote way, i.e., not in the immediate vicinity of the manipulator.
In order to govern manually the variations of the posture of the manipulator, the operator uses specific pushbuttons of the teach pendant, known as jog buttons or jog keys, which govern movement of one or more axes of the robot. By acting on the jog buttons of the teach pendant the TCP can be moved in a specific direction, whether positive or negative, within a reference system selected by the operator from among a plurality of possible reference systems. For instance, in an anthropomorphic robot with six degrees of freedom at least the reference systems “Joints”, “Base” and “Tool” are typically provided, where the system Joints refers to the joints of the robot (a vector in this system represents the angular positions of each of the joints) and the systems Base and Tool are cartesian reference systems, the former referring to the base of the robot and the latter to the end effector provided on the end flange of the robot.
As compared to teach pendants, manual guide devices enable the activity of programming of the robot to be rendered more intuitive since they basically consist of a sort of grip associated to the movable structure of the manipulator on which the programmer acts to get the manipulator itself to perform the desired movements in the programming stage. In general, associated to the aforesaid grip is a force sensor that enables the control unit to recognize the direction of displacement desired by the programmer (see, for example, U.S. Pat. No. 6,212,443 A). As an alternative or in addition to a force sensor a joystick device may be provided (see, for example, U.S. Pat. No. 8,412,379 B).
In the majority of known solutions, the control unit of a robot is able to operate according to three different modes or states, namely a Programming mode, an Automatic mode, and a Remote mode.
In the Programming mode, an operator acts in the vicinity of the manipulator, as explained previously, in order to govern operation thereof, store the programming steps, and program the operating activity, by means of the teach pendant or the manual guide device.
The step of programming of the robot is clearly the one that involves greater risks for an operator, who must follow closely the TCP in order to check visually positioning thereof, moving continuously around the manipulator. For this reason, in the Programming mode restrictions of speed to the movements of the manipulator are normally activated. In the case of use of a teach pendant, the operator has then available in his own hands an emergency-stop pushbutton and an enabling device, which are both present on the terminal. In practice, if in the programming stage the enabling device is not kept active manually by the operator, the manipulator cannot perform any movement. In the case of a manual guide device, the grip itself constitutes a sort of enabling device given that its release by the operator cause the movement of the robot to stop. However, it is preferable to provide an emergency-stop device and an enabling device also in manual guide devices.
In the Automatic mode, the robot executes an operating program of its own, obtained as explained above, possibly in combination with other robot or automatic apparatuses, normally within a cell protected from access of staff, but under visual control of an operator.
Also in the Remote mode, the robot executes an operating program of its own within a cell normally protected from access of staff, but in this case start of execution of the program comes from a cell supervisor, such as a PLC, which, for example, controls both the robot and other automatic apparatuses present in the cell itself.
Also in the case of machining operations executed via industrial robots in Automatic or Remote mode, it may prove useful or necessary for an operator to approach the working area of the manipulator or move within its range, for example for controlling visually the precision or effectiveness of certain operations carried out by the manipulator.
For these cases, it is known to provide suitable systems designed to detect the presence of an operator within the working area of the manipulator or in its vicinity. These systems may, for example, be based upon the use of devices for acquisition and comparison of images, or else may use laser scanners or light barriers designed to detect entry of the operator into the working area of the manipulator. In general, following upon the detection made, the surveillance system stops operation of the robot. The area surveyed may also be divided into areas of different degrees of criticality: in this case, the operator who moves into an area relatively close to the manipulator but still outside of its range of movement receives a visual or acoustic warning; if, instead, the operator enters a second area, corresponding to the aforesaid range of movement, movement of the manipulator is stopped.
An approach of this sort guarantees a high degree of safety for the operators but frequently causes interruptions of the production flow that would not strictly be necessary.